Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.96   13.639%   $255.6423   $255.64   $255.65   $255.60  
  Purchase #2 $174.62   3.218%   $180.2393   $180.24   $180.25   $180.20  
  Purchase #3 $88.36   8.702%   $96.0491   $96.05   $96.05   $96.00  
  Purchase #4 $65.25   5.565%   $68.8812   $68.88   $68.90   $68.90  
  Purchase #5 $109.58   6.312%   $116.4967   $116.50   $116.50   $116.50  
  Purchase #6 $92.72   12.724%   $104.5177   $104.52   $104.50   $104.50  
  Purchase #7 $183.98   9.389%   $201.2539   $201.25   $201.25   $201.30  
  7 purchase totals = $939.47       $1,023.0802   $1,023.08   $1,023.10   $1,023.00